The megafight the world's been waiting for is bigger than anything we've ever seen in combat sports. The last time there was this much hype surrounding a match-up was for Mayweather's bout against Manny Pacquiao in 2015, but today's boxing match will overshadow that in every aspect.

The American is as good as it gets with the gloves on, coming out of retirement to put his 49-0 professional record on the line. But McGregor is a winner. He's shown in his career if he wants something, he'll go and grab it. It's why he made history by becoming the first fighter to hold simultaneous titles in two weight divisions in the UFC.

"The Notorious" has never boxed professionally before, so the smart money's on Mayweather. He's paying $3.75 on Sportsbet.com.au to win by decision while McGregor's paying $4.35 to knock the American out. Everyone that's seen just how damaging McGregor's left hand can be is aware he only needs one punch to win the fight and shock the world.

British boxer Savannah Marshall dominated in her debut fight, recording a unanimous decision win in a four-rounder against Sydney LeBlanc.

The Mayweather Promotions-signed fighter was a world champion and Commonwealth Games gold medallist as an amateur and outclassed LeBlanc, whose record dropped to 4-4-1.

Late blows hit Team Mayweather

Floyd Mayweather Jr., left, and Conor McGregor exchange words during a news conference at Staples Center Tuesday, July 11, 2017, in Los Angeles. The two will fight in a boxing match in Las Vegas on Aug. 26. (AP Photo/Jae C. Hong)Jae C. Hong

Team Mayweather was forced to make a late adjustment on fight day after a daring disruption by Conor McGregor's fans.

The Irish have taken over Las Vegas ahead of today's megafight and they were up to mischief last night.

A TMT "The Money Team" billboard positioned on one of the major roads here was hilariously defaced.

The artists wrote 49-1 in large white numbers to reveal their prediction of what Mayweather's record - currently 49-0 - will be after today's fight. And finished the job by painting an Irish flag.

Workmen were forced to remove the flag and cover the writing early this morning.

McGregor's countrymen dominated the crowd at yesterday's weigh-in and were singing in the streets well into the night.

"There's a saying, you'll never beat the Irish," McGregor said. "You can't beat us. We roll in and take over wherever we want. Las Vegas is Ireland now."

The slight comes after Team Mayweather was dealt a crushing blow at yesterday's weigh-in when the American's protege - IBF super featherweight champion Gervonta Davis - was stripped of his title for failing to make weight ahead of his fight against Francisco Fonseca on Sunday's undercard.

Davis missed the 130-pound (60kg) limit by two pounds, ending any hopes he had of defending his belt. The fight will still go ahead but if Davis wins, his strap will remain unclaimed.

Mayweather Promotions represents the 22-year-old, who boasts an 18-0 record with 17 knockouts.

"There are a lot of fighters who are world champions who are not as big as Gervonta is," Mayweather once said about him. "He's connected to me but also he can fight. I would say this: Gervonta is not just the youngest world champion, he's one of the most exciting fighters in boxing."

This isn't the first time Davis has had weight troubles, needing three attempts to make weight when he first defended his title against Liam Walsh in May. Mayweather was ringside on that occasion, barking instructions at the youngster as he destroyed Walsh inside three rounds.

"Tank (Davis) is the future of boxing. He's me from a few years ago - same burning ambition," Mayweather said after that bout.

The undercard had already suffered a blow when former IBF welterweight champion Shawn Porter pulled out of his fight against Thomas Dulorme because of personal reasons including a death in the family. He has been replaced by 2008 Olympic Bronze medallist Yordenis Ugas.

Mayweather mocks McGregor's erection

Conor McGregor excited at the weigh-in.Source:Twitter

Both Mayweather and McGregor's bodies rated a mention as the pair weighed in on Saturday (AEST).

The boxing legend mocked the Irishman when he walked on stage with what looked like an erection, while Mayweather's nether regions also provided a talking point as he rocked green undies provided by an Irish bookmaker with some fine print: "Always bet on black."

McGregor was a pound under the 154-pound (70kg) limit when he stepped on the scales before Mayweather weighed in at a surprisingly light 149.5 pounds.

McGregor revealed on stage he expected to weigh around 170 pounds (77kg) when the bell sounded and ridiculed Mayweather for looking out of shape.

Mayweather had attempted to spread rumours about McGregor struggling to make weight, but he's never missed weight in his entire UFC career and he didn't start now.

"I'm a professional, I make weight. It's sacrifice, it's dedication, it's focus, but I make it," the Irishman said. "Look at me, I'm in peak physical condition. I've put in the work as everyone can tell. I'm ready.

"(I'll be) a lot bigger than him (by the time of the fight). I'd say close to 170, yes."

Firecracker waiting to explode

The hype machine has been in overdrive ever since the bout was confirmed in June. McGregor and Mayweather were at their trash-talking best during a world press tour that saw them trade verbal barbs in Los Angeles, Toronto, New York and London.

Their grand entrances into Las Vegas during the week weren't exactly quiet either, particularly for McGregor. He was involved in a scuffle with a member of the American's entourage before being confronted by bitter sparring partner Paulie Malignaggi, who took offence to the UFC icon's camp posting a photo of him on the canvas on social media.

Thursday's final press conference was more subdued. Both men knew by this time, whatever they said didn't matter - their fists were about to become far more important than their tongues.